Marine sponges and ascidians have proven to be a vast source of pharmacologically bioactive secondary metabolites. The need for new drugs for the treatment of diseases continutes to encourage research forthe isolation and characterization of novel natural products. We are interested in determining the precise cellular localization of these compounds to understand the basic cellular processes of metabolic pathways, biological, and ecological function. The role of associated microbial and algal symbionts in secondary metabolite production will also be studied. The class of compounds known as the pyridoacridines has been the subject of much biomedical and chemical interest due to their high bioactivity, interesting heterocyclic structures, and transphylogenic distributrion. We have found that some of these compounds undergo a characteristic color change with a change in pH in both visible light and fluorescence emmision. We propose to utilize this feature as a marker while using laser scanning confocal microscopy to study the cellular localization of pyridoacridines in sponge and ascidian tissues. Various sponge and ascidian samples whose chemistry has been previously determined were examined using confocal microscopy to determine the feasibility of utilizing this method as a means of studying the cellular localization of their secondary metabolites. Once a good candidate was found, differential staining methods were developed to investigate the localization of compounds within specific cells. The results of these studies will direct future sample collection and preservation procedures for continued research involving confocal microscopy methods in marine natural products chemistry. The results of this research will aso influence the development of methods to test the biological and ecological functions of the localized secondary metabolites from marine invertebrates. This project is near to completion and a manuscript is in preparation.